Photo-induced charge state conversion of Eu2+ in Ca2ZnSi2O7

概要

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Eu2+ doped sorosilicate Ca2ZnSi2O7 (melilite) exhibits a broad band emission peaking at ~600 nm (~2 eV) due to the electric dipole allowed transition of 4f65d1 to 4f7 of Eu2+ by an excitation with blue light (460 nm). Strong O2− ligand field with low symmetry due to the layered tetragonal crystallographic structure of the melilite may play a dominant role in lowering the emission band energy to ~2 eV. In addition, line emissions attributable to the transitions from 5D0 to 7FJ of Eu3+ ions are detected by an excitation with deep UV light with sub-360 nm wavelengths. This is due to the formation of transient Eu3+ ions via charge transfer from Eu2+ to the matrix. The lifetime of the transient Eu3+ ion is found to be 58 ms by a pump-probe measurement, in which UV pulse laser and green continuous wave laser are employed as pump and probe lights, respectively. Based on these results, the energy diagram of Eu2+ in Ca2ZnSi2O7 is proposed.